In a wavelength division multiplex-passive optical network (WDM-PON), data is transferred in a manner that the optical network unit (ONU) exclusively uses the upstream/downstream wavelengths. In the WDM-PON, different ONUs on the user terminal adopt different operation wavelengths, i.e., the carrier wavelengths used by ONUs for sending the upstream data are different. In order to avoid the case that the ONU devices are different result from lasers of different wavelengths are to be arranged on the ONUs, a colorless ONU needs to be implemented in the WDM-PON. The colorless ONU means that all ONU devices on the user terminal are totally the same, and the ONU devices do not need to be configured with a corresponding laser according to the operation wavelength respectively to provide a carrier light source.
At present, the method for implementing the colorless ONU includes: arranging a continuous broadband light source in an optical line termination (OLT); performing spectrum slicing on a remote node to generate narrow linewidth light sources with a demultiplexer; sending the spectrally sliced wavelengths to the ONU; injection locking or reflective amplifying the spectrally sliced wavelength by the ONU, so that it may be used as the carrier light sources for the upstream data and send the upstream data to the OLT.
Although in the prior art, it is avoided to arrange a laser with specific wavelength in the ONU, a high power broadband light source is required. Furthermore, large amount of energy is wasted when spectrally slicing the broadband light source, so that the cost of data transfer is increased.
Another existing method for implementing the colorless ONU includes using a downstream light as the carrier for upstream data. The downstream optical signal is injection locked or reflective amplified by the ONU, and then the upstream data is modulated onto the amplified downstream light. The synchronization between the downstream optical signal and the upstream data is achieved by adding a synchronization device such as a clock recovers. For making it possible for the ONU to perform injection locking or amplifying the downstream optical signal, it is required that the optical power for the downstream optical signal during each downstream bit can be ensured to be locked or amplified, and when the downstream optical signal has the lowest optical power, i.e., when the downstream data is 0, the optical power of the corresponding downstream optical signal can be locked or amplified. When the upstream data is modulated in the prior art, the optical power of the downstream optical signal corresponding to the downstream data is regulated to increase the optical power of the corresponding downstream optical signal when the downstream data is 0.
It can be seen that although the downstream light may be used as the carrier light source for the upstream data in the prior art, the existing devices need to be modified, and a synchronization device needs to be added, which increases the complexity and cost of the devices. Furthermore, although the optical power of the corresponding downstream optical signal is increased when the downstream data is 0 in the prior art, the extinction ratio of the downstream optical signal and the transmission performance are sacrificed, which causes an increase of the bit error rate of the downstream data, and makes it difficult to determine the downstream data.
It can be seen that in the existing method for implementing the colorless ONU, the complexity of the system as well as the cost of the devices are increased, and the requirements of the WDM-PON applications cannot be met.